On Tue, Jul 13, 2010 at 5:26 PM, Paolo Bonzini <bonz...@gnu.org> wrote: > On 07/13/2010 04:53 PM, Richard Guenther wrote: >> >> On Tue, Jul 13, 2010 at 4:50 PM, Paolo Bonzini<bonz...@gnu.org> wrote: >>> >>> On 07/08/2010 10:58 PM, Maxiwell Garcia wrote: >>>> >>>> Hi, >>>> >>>> I am writing a paper about instruction-set architecture simulators. In >>>> first time, I used gcc-4.4.0 and the compilation time reached 33 >>>> minutes (with -O3) for my simulator and the performance reached 270 >>>> MIPS (Million instruction per second). When I used the gcc-4.4.4, in >>>> the same code, the compilation time reached 39 seconds and the >>>> performance reached 600 MIPS. My code have many "switchs" with 512 >>>> "cases" and the library<systemc.h> is in use. >>>> How to explain this behavior in the compilation and performance in my >>>> paper? >>> >>> Try -ftime-report, it should explain the compilation time change. Such a >>> dramatic performance change is usually due to better register allocation, >>> but this is just a guess. >> >> I would guess it was the various backports of tree PRE fixes actually. > > Sorry, I was referring to the change in performance which I justified by > better register allocation. PRE is indeed a good candidate for the > compilation time fixes. Could the changes to PRE cause different code to be > generated?
Yes, they will generally cause more PRE to be performed. What ends up generating the noticeable performance difference depends on the specific testcase though - and it might very well be RA (and 4.4.0 to 4.4.4 is a significant amount of changes). Richard. > Paolo >
